2023 Mid-Atlantic Severe Wx Thread (General Discussion)

[AdamHLG]

I’m ready. Let’s do this.


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[H2O]

No sun by 10:15am here?  bust

 

[yoda]

 

 

[nj2va]

Can someone explain/remind me what a hatched area means?  

[TSG]

Just now, nj2va said:

Can someone explain/remind me what a hatched area means?  

10% chance of winds in excess of 65kts

[yoda]

2 minutes ago, nj2va said:

Can someone explain/remind me what a hatched area means?  

Hatched Area: 10% or greater probability of wind gusts 65 knots or greater within 25 miles of a point

[jewell2188]

Been full sun last hour in culpeper. Certainly Has that “feel” today but we shall see. 

[Kmlwx]

I'm in favor of keeping it all here - while it turns into a mega-thread most years - it's a one stop shop for those wishing to go back through prior year's severe events. I know we used to separate into threads - but it's tougher to search those out than a single thread. And I don't think the forum struggles with large threads as much as it used to. 

[yoda]

Tornado Watch coming soon out west 

 

 

   Mesoscale Discussion 1877
   NWS Storm Prediction Center Norman OK
   0919 AM CDT Mon Aug 07 2023

   Areas affected...portions of eastern Kentucky into far southern Ohio
   and western West Virginia

   Concerning...Severe potential...Tornado Watch likely 

   Valid 071419Z - 071545Z

   Probability of Watch Issuance...95 percent

   SUMMARY...The severe threat is increasing across portions of the OH
   Valley into the central Appalachians. Several instances of damaging
   winds are expected along with a few tornadoes. A Tornado Watch will
   be likely be needed soon.

   DISCUSSION...The boundary layer is destabilizing across portions of
   the TN/OH Valleys into the central Appalachians, with surface
   temperatures approaching 80 F amid 70+ F dewpoints, yielding
   1500-2000 J/kg MLCAPE amid eroding MLCINH. At the same time, an 80+
   kt 300 mb jet is rounding the base of the trough, encouraging strong
   700 mb WAA and associated convective initiation across northern TN
   into southern OH. These storms should increase in coverage and
   intensity through the late morning/early afternoon hours. The 12Z
   BNA sounding showed a hodograph with strong low-level curvature and
   elongation, indicative of strong vertical shear coinciding the warm
   sector. 

   As the upper trough and associated strong low-level flow shunt
   eastward toward the central Appalachians, many of the intensifying
   storms should become supercells, which will quickly merge into line
   segments. Several instances of damaging gusts and a few tornadoes
   are likely given the favorable overlapping buoyancy/vertical shear
   space. A Tornado Watch will likely be needed soon to address the
   impending severe threat.

   ..Squitieri/Guyer.. 08/07/2023

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...PBZ...RLX...MRX...JKL...ILN...LMK...OHX...

[mappy]

22 minutes ago, Eskimo Joe said:

12z NAMNest slams Baltimore. Mature bowing structure goes right through their metro right at peak heating.

you have timing on that? I can't check right now.

 

Also -- agree on keeping things here vs a new thread. 

[yoda]

2 minutes ago, mappy said:

you have timing on that? I can't check right now.

 

Also -- agree on keeping things here vs a new thread. 

22z to 23z time period 

[09-10 analogy]

24 minutes ago, Eskimo Joe said:

Next 1 to 3 hours will be key. I don't want to see us get stuck with pre-frontal convection that kills instability off or persistent low clouds. 

That always seems to be a threat. Still high clouds here; I’m beginning to temper expectations for my back yard. Still think it’ll be a big day for MA overall

[mappy]

4 minutes ago, yoda said:

22z to 23z time period 

Thank you! I'm obviously the one to keep an eye on things for the dance studio  

[TSSN+]

Low cloud deck seems to be sweeping east of Frederick now. Should start to see more sun in the next hour. 

[yoda]

 

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1028 AM EDT Mon Aug 7 2023

.SYNOPSIS...
Scattered to numerous strong to severe thunderstorms are expected
today as a strong cold front pushes through the region. High
pressure returns behind the front Tuesday into Wednesday with breezy
conditions. A warm frontal boundary approaches from the south
THursday into Friday bring additional showers and thunderstorms.
Unsettled conditions linger into the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
The forecast remains on track with a mesoscale convective vortex
(MCV) lifting toward northwestern Pennsylvania. Some residual
showers are pushing through Garrett, Mineral, and Allegany
counties, but these are decaying with little to no lightning
left. Elsewhere, a stagnant area of stratus clouds sit from the
I-64 corridor northeastward into northern Virginia, as well as
the DC/Baltimore metros. However, the aircraft soundings (ACAR)
do show this low cloud deck being quite shallow in nature with a
depth of about 200 meters (~650 feet). Given the early August
solar insolation angle, these should burn off/erode within the
next hour or two. Farther west, the Shenandoah Valley is under
mainly sunny skies with convective initiation likely within the
next few hours.

Daytime heating brings temperatures into the upper 80s to low
90s. Combined with dew points in the low to mid 70s, expect peak
heat indices between 100- 105 east of the Blue Ridge, and 95-99
west. This moist and unstable environment will fuel the active
weather looming later in the day. Of note, the Storm
Prediction Center has upgraded the risk area to Moderate which
is seen only 2 to 3 times per decade in the area.

Looking ahead at this afternoon and evening, given that we
destabilize, all signs point to a likely widespread severe wind
event across our area, though all modes of severe weather are
possible. A large mid-level trough over the western OH Valley this
morning will move eastward toward the Central Appalachians, with two
surface lows noted early this morning - one over southern ON and the
other along the IN/IL border. These surface lows deepen through the
afternoon, with models indicating pressure in the low 1000mb range,
which is quite impressive for early August (for a non-tropical low).
Storms are expected to develop in a favorable environment today
where surface dew points in the low 70s and impressive mid-level
lapse rates of 6-7 C/km yield around 1500-2000 J/kg of MLCAPE
(SBCAPE up to 2500+ J/kg possible). Storms should easily become
organized with deep-layer shear of 35-50KT.

Multiple rounds of storms are likely to impact the area today. The
moist airmass, approaching PVA max, and remnant MCV could initiate
late morning to early afternoon activity west of I-81 into north-
central MD. There is some potential for a storm or two to become
severe, with damaging winds and hail as the main threats.

The main surge is expected to develop by mid afternoon as the strong
synoptic forcing arrives, and is enhanced by the existing terrain
circulation and lee-side pressure trough. Models are rather good
agreement on timing, indicating numerous storms developing west of
the Blue Ridge between 2PM-3PM. These initial semi-discrete/cluster
storms could pose a large hail threat, in addition to damaging wind
gusts and a tornado or two. These storms move east of the Blue Ridge
between 4PM-5PM, and likely congeal into a solid/quasi-solid line
that reaches the I-95 corridor between 6PM-7PM.

This QLCS will be capable of producing widespread damaging wind
gusts, in addition to the possibility of embedded QLCS tornadoes.
Tornadoes that develop within these squall lines typically have
little lead time due to their rapid genesis. It is important to take
immediate action if a Tornado Warning is issued for your area. The
hail threat should diminish as the line of storms pushes eastward.

Finally, as the main mid-level trough moves over our area it could
initiate an additional broken line of showers and thunderstorms
later this evening. A low-level jet will have developed by that
time, and model soundings respond to the increasing low-level shear
with very wide hodographs, especially east of the Blue Ridge. There
will be a conditional tornado threat that lasts past sunset, and
given the strong shear, it won`t take much instability for these
storms to intensify.

Be sure you have multiple ways of receiving severe weather alerts
today, and take immediate action if a severe thunderstorm or tornado
warning is issued for your location.

[WxWatcher007]

Yeah, I don’t think this is one of those days where cloud cover throws a big wrench into things. Like EJ said earlier, I think it’s more likely the soundings are oriented a little differently than initially proved but don’t see evidence of that either currently. 

It’s a hurry up and wait kind of day.

[jewell2188]

Been a while to see such juicy discussions from NWS!!!!! 

[Eskimo Joe]

Per the 12z sounding from IAD, today's convective temp is 90 degrees. We have a ways to go for heating if we want to maximize potential.

[09-10 analogy]

I always like second rounds.

Somewhat lost in the excitement, maybe, but we haven’t had too many days this summer with HIs over 100, as mentioned in the AFD.

 

[Eskimo Joe]

Thursday could another active day, but let's focus on today first.

[TSSN+]

Mostly sun now in Westminster with just some low clouds burning off. 

[SomeguyfromTakomaPark]

 

[jewell2188]

Seems to be differing opinions on the impact of cloud cover today. 

[dailylurker]

17 minutes ago, WxWatcher007 said:

Yeah, I don’t think this is one of those days where cloud cover throws a big wrench into things. Like EJ said earlier, I think it’s more likely the soundings are oriented a little differently than initially proved but don’t see evidence of that either currently. 

It’s a hurry up and wait kind of day.

But we need sun if we're getting a wedge through the swamp. Thick clouds here in AA County. I'm off work today so I'm going to head out 70 and get in position early. I hope to stay out ahead of the storm and then if a warning pops I'll be in range to chase. If it's intense straight line winds then I'm going to try to position myself to experience the full force of whatever it's producing. 

[WxWatcher007]

1 minute ago, dailylurker said:

But we need sun if we're getting a wedge through the swamp. Thick clouds here in AA County. I'm off work today so I'm going to head out 70 and get in position early. I hope to stay out ahead of the storm and then if a warning pops I'll in in range to chase. Getting in the truck now. 

Good luck chasing today. 

[yoda]

Large tornado watch posted out west

 

   URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 599
   NWS Storm Prediction Center Norman OK
   1055 AM EDT Mon Aug 7 2023

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     Central and Eastern Kentucky
     Southern Ohio
     Southwest Pennsylvania
     Western Virginia
     West Virginia

   * Effective this Monday morning and evening from 1055 AM until
     600 PM EDT.

   * Primary threats include...
     A few tornadoes possible
     Widespread damaging wind gusts to 70 mph likely
     Isolated very large hail events to 2 inches in diameter possible

   SUMMARY...A very favorable scenario for intense supercell storms
   exists today, and severe storms are expected to develop and increase
   by midday/early afternoon across the region. A few tornadoes will be
   possible, along with hail and potentially widespread damaging winds,
   particularly later this afternoon as storms approach the
   Appalachians.

   The tornado watch area is approximately along and 100 statute miles
   east and west of a line from 50 miles north northeast of Parkersburg
   WV to 45 miles southwest of London KY. For a complete depiction of
   the watch see the associated watch outline update (WOUS64 KWNS
   WOU9).

[TSG]

Low clouds are quickly disappearing across NoVA, less so south of 64

[nj2va]

I'm good if DC stays under clouds all day - don't want severe after last weekend.

[LeesburgWx]

Here in Reston right now and multiple blue sky patches and sun breaking out now

[Kmlwx]

Visible satellite shows steady thinning of the cloud cover.